Pressure difference measuring transducers comprise a measuring mechanism equipped with a pressure difference sensor and having two membranes to be loaded, respectively, with the two pressures during operation. For this in industrial measurements technology, two measuring mechanism variants have become established, which differ from one another in the arrangement of the membranes.
In the case of the first measuring mechanism variant, the two membranes are arranged in a plane next to one another on one and the same external surface of the measuring mechanism. In the case of this variant, the membranes are isolating diaphragms, which, in each case, outwardly terminate one of the pressure transfer means connected before the pressure difference sensor and transferring the pressure acting on the outside of the isolating diaphragm to the pressure difference sensor.
In the case of these measuring mechanisms, the face of the measuring mechanism surrounding the two membranes can be embodied as a process connection flange, via which the pressure difference measuring transducer can be mounted on a process connection provided at a measuring point and connected to working pressure lines, via which the membranes are contactable during operation with the two pressures. Such a pressure difference measuring transducer is known e.g. from German patent, DE 10 2014 102 719 A1. The pressure difference measuring transducer described there is mounted on a process connection of a valve block with interpositioning of a plate-shaped spacer.
Alternatively, there can be provided on the face of measuring mechanisms of the first variant containing the isolating diaphragms a front cover, under which are enclosed on its inner side, arranged in a plane next to one another, two pressure chambers, each of which adjoins one of the two isolating diaphragms, and on whose outside a process connection is provided, via which the pressure difference measuring transducer can be mounted on a process connection provided at a measuring point and connected to working pressure lines.
In the case of the second measuring mechanism variant, the two membranes are arranged on external sides of the measuring mechanism lying diametrically opposite one another. The membranes of the second measuring mechanism variant can likewise be isolating diaphragms of the pressure difference sensor connected in front of pressure transfer means. Alternatively, they can, however, also be medium resistant membranes of the pressure difference sensor mounted in the measuring mechanism. Thus, for example, in German patent, DE 103 47 861 A1, a pressure difference measuring transducer is described having mounted in a measuring mechanism a ceramic pressure difference sensor, whose measuring membranes form the membranes to be loaded with pressure and arranged on the oppositely lying, external sides of the measuring mechanism.
Measuring mechanisms of pressure difference measuring transducers comprising this second variant are usually equipped with a flange-set, which includes two flanges to be mounted on the two, oppositely lying, external sides of the measuring mechanism. Thus, described, for example, in DE 103 47 861 A1 is a flange-set, which has, mounted on the two oppositely lying, external sides of the measuring mechanism, two flanges, each of which comprises                a wall, which in the mounted state covers one of the two membranes of the measuring mechanism and encloses a pressure chamber bordering on such membrane, and        arranged on a first of four, pairwise oppositely lying sides of the wall, a first process connection, which includes a pressure duct connection region, into which opens a pressure duct extending through the flange to the pressure chamber.        
The flanges described in DE 103 47 861 A1 include, in each case, an identically formed, second process connection arranged on its side lying opposite the side containing the first process connection. This offers the advantage that the pressure ducts opening into the two process connections not required for mounting can be utilized, in order, when required, to ventilate the pressure chambers or to let condensate escape.
Such a ventilation, or the draining of condensate, is in the case of pressure difference measuring transducers with measuring mechanisms of the first variant not directly possible. The problem is that the pressure chambers adjoining the membranes are arranged here in a plane next to one another, as well as that, on the side of the front covers lying opposite the process connection, two other process connections cannot be directly provided for aerating the pressure chambers or removing condensate, because the measuring mechanism is located on that side.
In the case of measuring mechanisms of the first variant, the membrane centers of the membranes arranged next to one another in a plane have a separation, which is less than the separation between the membrane centers of membranes arranged on external sides of measuring mechanisms of the second variant lying opposite one another.
This has led to the result that, for the mounting and connection of pressure difference measuring transducers, two different process connection geometries have been established, which differ in the arrangement of their pressure duct connection regions. In such case, the two pressure duct connection regions of process connections with a first process connection geometry established for the connection and mounting of pressure difference measuring transducers with measuring mechanisms of the first variant are arranged with a smaller separation from one another than the two pressure duct connection regions of process connections with a second process connection geometry established for the connection and mounting of pressure difference measuring transducers with measuring mechanisms of the second variant. Established as second process connection flange geometry in industrial measurements technology is the flange connection geometry detailed in DIN EN 61518 of the German Institute for Standardization and in the corresponding standard IEC 6158 of the International Electrotechnical Commission.
Due to the different process connection geometries, measuring transducers with measuring mechanisms of the second variant cannot be applied directly onto process connections provided for measuring transducers with measuring mechanisms of the first variant.
This problem can in some cases of application be overcome by connecting measuring transducer and process connection with one another via an adapter arranged therebetween, which adapter is embodied in such a manner that it interfaces the second process connection geometry present on the measuring transducer side into the first process connection geometry provided on the measuring point side.
The interposing of an adapter causes, however, additional costs and an additional assembly effort. Moreover, a pressure tight sealing of the two pressure transfer paths extending through the adapter both between the adapter and the measuring transducer, as well as also between the adapter and the measuring point process connection, must be assured. Moreover, an adapter can only be applied, when sufficient space for the adapter is present at the location of use.